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E39 (1997 - 2003) The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

I have a new to me this Christmas a 528i meticulously maintained. 190k or 188k miles. I was driving around home today and noticed that my temp gauge was suddenly sitting in the red area. I limped about 2 miles home and shut it off. Let it cool down an hr or two then topped up the expansion tank. It was down only a cup or 2. I fired it up Revved for a minute r so. The gauge was at normal. I drove around the block maybe twice then the gauge stared to climb. Got it in the garage just as it hit red again and shut it off. The rad hose back into the thermostat was cool and out to the rad the hose was very hot. No expansion tank leaks. The hoses were soft and squish able. It seemed like a t stat or water pump sudden failure.

The previous owner had great records so I looked them up and the same issue happened only 11k miles ago and he had the t stat. Water pump and thermostat and all gaskets and vent screws changed at the BMW dealership where he bought it. Now I am stumped as to what this may be. Any ideas???

When you "topped off" the expansion tank, did you loosen the bleed screw first? The 6s are more bleed-fussy than the V8s. I had a friend ruin the head gasket on an E34 520i (living in Europe at the time), because on a long drive he "topped off" and then drove in the red for several hundred KMs thinking there was coolant in the system. As soon as we loosened the coolant screw, it was obvious that his coolant system was full of air. Alas, too late; the white smoke and antifreeze in the oil appeared a short time later.

How long have you driven the car since getting it? If this issue has never occurred before, you can probably eliminate air in the system as an issue. Is your aux fan kicking on? Does this happen every time you drive? The T-stat & W-pump are less likely causes due to recent replacement. Is your belt system operating properly? A failed tensioner or pulley could cause slack in the belt system causing the WP to become ineffective. Check it.

Thanks Fudman. I have put only about 200miles on the car since I got it. It has never happened until last night. I followed the bleed procedure to the letter as it spewed out a bit of coolant on my 2 mile limp home. Since the bleed it appears to be fine. I ran it last night 2am! And no issues. The expansion tank only dropped about 1-2 inches below the filler neck when I checked this am. Just got back from a 1/2 hour drive and the gauge is right where it should be. I'll check the tank later. I think your onto something as after having the dealer change those parts 11k ago something must be going. I will keep digging

I noticed that after my drive today. And last night for that matter, the hose going from the rad to the t stat housing was not warm at all. Does the rad really cool off the coolant that much? It was 26 F at the time outside

What kind of water pump was installed? Just because it's new doesn't rule it out. I put in a new Bosch water pump last spring that went to crap in December. The plastic impeller cracked and it was loose on the shaft. It would do ok around town but would begin to overheat within a few miles of highway driving.
Not sure if thats your case though with the cool hose on the bottom, but definitly something to keep in mind if it has a Bosch waterpump.

First don't drive the car when overheating the 6 is between 90-100 degrees c operating temp and your needle on the cluster will not begin to move until 117 so if it was in the red when u drove it. It was way overheated.
second if u have no issues after bleeding then u r all good if you drive it for a few days or weeks and the same problem occurs my oppinion is that u have a small leak somewhere thus allowing air to slowly enter the system. If problem continues after hoses,radiator,waterpump,ect ect has been checked for leaks. 1.take out thermostate and drill a 1/16 inch hole on the top of the tstat and reinstall 2. Check your head gasket. It might not b showing typical sighns. Ex. Milky oil, burning antifreeze out of exhaust, constantly adding antifreeze. But rather u may have a small leak on the exhaust port on the HG not allowing large amounts of antifreeze into the system but minor amounts. And small amounts of air that build up over weeks or months depending on how often and Lon u drive the car.

Dilli: no clue as to what was installed but as I said all work was done by a large BMW dealer I am thinking allparts are BMW. I could be a premature failure.

Mcsimon: it was below freezing and I only hit 1-1.5k rpm in the mile or so I limped. I hope it's fine! This just happened last night so I am on a run
,test, check mode today and will be till I find the culprit. I am suspecting a small air leak as another possibility but it will take some time and monitoring.
How do you "check" the head gasket without pulling the head?

Kmorgan: had the heater turned way down but after my bleed, the gauge and heat from the heater were fine

I still would like to know what is the standard temp for the hose going from the rad back into the motor. After my test drives, both times I check it by grabbing and squeezing it and it was room temp or even a bit cooler. Like no coolant is flowing but the temp gauge says it running normal. Do BMW rads work that well?? No hissing out the vent hole or very warm rad cab like went it first spiked. Now they seem fine too. Just puzzling I though any return water line to a liquid cooled engine should be at least a little warm to the touch....

One thing you can do that sometimes gives a clue to the head gasket is to drain a little bit of oil into a glass jar. If there is any coolant in there it is usually in the bottom of the sump (cool engine) and you can see it in the bottom of the jar. You can also just lift out the oil filter and take a close look at the oil on the filter. If it looks milky that is a bad sign.

One thing you can do that sometimes gives a clue to the head gasket is to drain a little bit of oil into a glass jar. If there is any coolant in there it is usually in the bottom of the sump (cool engine) and you can see it in the bottom of the jar. You can also just lift out the oil filter and take a close look at the oil on the filter. If it looks milky that is a bad sign.

Good luck.

Thanks for the info. So you think the gasket and head could be damaged driving in the red for a mile or two at 1k rpm? I know it wasn't any further. Just asking. I have been driving off and on today and the coolant has not dropped below where it was first thing this am after last nights bleed and test run

I wasn't implying that you damaged the HG by driving while hot but maybe that was the cause of the overheating to begin with. No way to know but to just start checking and eliminating things as you go.

I wasn't implying that you damaged the HG by driving while hot but maybe that was the cause of the overheating to begin with. No way to know but to just start checking and eliminating things as you go.

Ahh I see. I will check when I get home. Did the OB test and its running around 95-97 with a good hi rev run for 15 minutes. The expansion bottle has not dropped from where I marked it after my bleed and test run last night. It just might be time for a cooling system overhaul because at 118k Miles's all I have proof of is that the t stat and pump were changed. Replace it all for piece of mind I am thinking!

I drained out the coolant this eve as the coolant and water I topped it up with at 3 am last night was Questionable. Even after that fill I bleed it and had no issues on test run last night. Expansion bottle was full this morning. After driving it around today no issues but running at 97-98 that's when I decided to drain everything out as I grabbed distiller water and extended life prestone. Hey I am still trouble shooting!! Anyway I filled and bleed it and now runs at 94. Air isn't the issue as I dumped in 9 litres of mix, bleed it and drove for and hr right out of the shop with only the OBD readout as my guide. 94 solid. Expansion bottle dropped maybe an inch. All in all seems very solid now. My question remains what " caused" it to spike last night. Coolant may have been low causing an air pocket but I haven't checked it for a while because the gauge had always been ok. Till last night

I am on this like white on rice now to monitor any changes in temp or coolant drop. I am sure the rad is stock as is the fan clutch so I think I'll change those as today. I learned how.

. The rad hose back into the thermostat was cool and out to the rad the hose was very hot. No expansion tank leaks. The hoses were soft and squish able. It seemed like a t stat or water pump sudden failure.

The previous owner had great records so I looked them up and the same issue happened only 11k miles ago and he had the t stat. Water pump and thermostat and all gaskets and vent screws changed at the BMW dealership where he bought it. Now I am stumped as to what this may be. Any ideas???

This here to me sounds like a t-stat. If your water pump failed you would have hot on both hoses. At least for me that happen when the Bosch pump failed. I would recommend that you replace t-stay and fully bleed your cooling system and try it.

There's good reasons to use plastic impellers…. that's not the subject here though.

Generally speaking, the BMW cooling systems are known for failure. Replace it all, or run the risk of warping your head.

Well the subject was an overheating BMW which could have been caused by a failed plastic impeller, so it could be the subject. Anyway, I am interested to know the good reasons to use the plastic impellers...

Well after I drained the coolant and bleed I have been driving around for 3 days. The temp has never shown more than 95 degrees usually 94 and zero coolant has dissappered from the expansion tank. Seeing as how the thermostat and pump were changed 11k miles ago, I am going to change out the rad expansion tank and fan clutch. Then call it a day. I have no proof those have been changed

I did notice when I drained out all the coolant it was Prestone Green. Not BMW blue. Previous owner had the t stat and water pump changed at a BMW dealership and they put in Prestone???? Scam artists!

I am having the exact same issue with my 2000 528. 2 weeks ago the temp gauge pegged in a matter of 30 seconds while city driving in cold weather. I assumed the Tstat that I installed a month ago was bad and stuck closed. I put a new one in (btw the guys at BMA say that they rarely see new Tstat failers) and bled the system an hour ago... temp came up and held at the 12 o'clock position at idle in the garage.. test drove it (15F here) and within a minute it rapidly started over heating.. limped home and while under the hood I noticed that, just like your problem, the lower radiator hose was cold, while the upper was very hot. I didn't see any real explanations for this from any of the replies to your thread, but as for me and how I'm addressing my problem, it almost has to be the water pump. I've ruled out Tstat with two new ones, and if your lower hose was as cold as mine is, we would almost certainly be able to see momentary drops on the temp gauge as that cold coolant is pumped into the engine... if the pump were working. l'm not too thrilled about putting a new pump on, but I can think of no explanation other than the water pump... or the ruled out Tstat.. why our lower hoses are cold while the engine is on its way to "melt down".

I am having the exact same issue with my 2000 528. 2 weeks ago the temp gauge pegged in a matter of 30 seconds while city driving in cold weather. I assumed the Tstat that I installed a month ago was bad and stuck closed. I put a new one in (btw the guys at BMA say that they rarely see new Tstat failers) and bled the system an hour ago... temp came up and held at the 12 o'clock position at idle in the garage.. test drove it (15F here) and within a minute it rapidly started over heating.. limped home and while under the hood I noticed that, just like your problem, the lower radiator hose was cold, while the upper was very hot. I didn't see any real explanations for this from any of the replies to your thread, but as for me and how I'm addressing my problem, it almost has to be the water pump. I've ruled out Tstat with two new ones, and if your lower hose was as cold as mine is, we would almost certainly be able to see momentary drops on the temp gauge as that cold coolant is pumped into the engine... if the pump were working. l'm not too thrilled about putting a new pump on, but I can think of no explanation other than the water pump... or the ruled out Tstat.. why our lower hoses are cold while the engine is on its way to "melt down".

It would point to a t stat or water pump issue to explain the cold return hose but I was staying at 94 95 degrees. I did a third test but went out for 1/2 hr and the return hose was warm. I am suspecting that the t stat was opening just a bit to keep the temp at 94 as the first two tests were only 8 or so minutes and I watched the temp steadily increase and stop at 94. It was -5c outside (20 f?) and again these were short haul trips. I did a couple of 120 mile trips no issue but ordered the rad expansion tank and clutch anyway. Sure enough I noticed a slight crack in the t stat housing yesterday! Replacing that too!